1. Field of the Invention
This invention relates to Light Emitting Diodes (LED), and, more particularly, to an LED assembly and a method of fabricating the same.
2. Description of Related Art
With the progress of electronic industry and the advent of digital age, electronic products are designed to have a variety of functionalities. In recent years, eco-friendly electronic products such as light emitting diodes (LED) come to the market.
The LED chip is available in two configurations: (a) with both its +ve & −ve contact terminals (bond pads) on the same surface, shown as 10 in FIG. 1A; (b) with its +ve & −ye contact terminals (bond pads) on the opposite surfaces, shown as 10′ in FIG. 1B. As the LED technology is advancing, several packaging and architectures are now available accommodating both these configurations. FIGS. 1A, 1A′ and 1B show three different interconnect approaches in typical LED packages 1, 1″ and 1′ according to the prior art.
As shown in FIG. 1A, in the fabrication of the LED package 1 an LED chip 10 is disposed through an adhesive 102 on a substrate 12 having an inner circuit (not shown) and conductive pads 120; a wire bonding process is performed to electrically connect the electrode pads 100 of the LED chip 10 to the conductive pads 120 with gold wires 11; a light-pervious encapsulant 13 is formed on the substrate 12 for encapsulating the wire-bonded structure and a phosphor layer 14 is further formed over the light-pervious encapsulant 13, in more than one form or combination with the option to dispose the LED package 1 on and electrically connected to a circuit board (not shown).
As shown in FIG. 1A′, in the fabrication of the LED package 1″ the wire bonding process is eliminated and is replaced by ‘flip-chip interconnect’. In this case metal electrodes (also known as ‘bumps’) are implanted on the electrode pads 100 of the LED chip 10 and are used to electrically connect the LED chip 10 on a substrate 12 having an inner circuit (not shown) to the conductive pads 120.
In the fabrication of the LED package 1′ shown in FIG. 1B, an LED chip 10′ is disposed through an electrically conductive adhesive 102 on a substrate 12 that has an inner circuit (not shown) and conductive pads 120 and 121 An electrode pad 101 formed on a bottom side of the LED chip 10′ is electrically connected to the conductive pad 121; and a wire bonding process is performed to electrically connect an electrode pad 100 on a top side of the LED chip 10′ to the conductive pad 120 with a gold wire 11. A light-pervious encapsulant 13 is formed on the substrate 12 for encapsulating the wire-bonded structure and a phosphor layer 14 is formed over the light-pervious encapsulant 13 in more than one form or combination with the option to dispose the LED package 1 on and electrically connected to a circuit board (not shown).
In the LED packages 1 and 1′, since the electrode pads 100 are electrically connected to the conductive pads 120 with the gold wires 11, the substrate 12 that has the conductive pads 120 and 121 is needed for the conduction of the LED chips 10 and 10′. Therefore, the LED packages 1 and 1′ have an increased overall height due to the use of the substrate 12 having a thickness h and the arc-shaped gold wire 11. However, in the LED packages 1″ the height constraint due to the use of gold wires is eliminated, but the substrate still prevails.
Moreover, the conductive pads 120 and 121 of the substrate 12 have to be formed in accordance with the LED chips 10 and 10′ and the circuit board, and thus sizes and pitches thereof have to be adjusted from one product to another. As such, the LED packages 1 and 1 are costly to fabricate.
Because the adhesive 102 needs to be disposed between the LED chips 10 and 10′ and the substrate 12 and the substrate 12 is generally made of ceramics or plastics, the LED chips 10 and 10′ have poor heat-dissipating efficacy.
Therefore, how to overcome the problems of the prior art is becoming one of the critical issues in the art.